Aircraft equipped with sustaining rotors



June 27, 1944..

H. F. PITCAIRN AIRCRAFT EQUIPPED WITH SUSTAINING ROTORS Original FiledAug. 1, 1940 3 Sheets-Sheet l W FM ATTORNEYJ' June 27, 1944. Y H, F.PITCAIRN 2,352,342

AIRCRAFT EQUIPPED WITH SUSTAINING ROTORS 3 Sheets-Sheet2 Original FiledAug, 1, 1940 ATTORNEY;

June 27, 1944. p c I 2,352,342-

AIRCRAFT EQUIPPED WITH SUSTAINING ROTORS Original Filed Aug. 1, 1940 5Sfieets-Sheet s INVENTOR M91 fM BY W 7" Mon ATTORNEYS Patented June 27,1944 AIRCRAFT EQUIPPED WITH SUSTAINING ROTORS Harold F. Pitcairn, BrynAthyn, Pa., assignor to Autogiro Company of America, Willow Grove, Pa.,a corporation of Delaware Substituted for abandoned application SerialNo.

349,049, August 1, 1940. This application November 2, 1940, Serial No.363,997

Claims.

This invention relates to aircraft equipped with one or more sustainingrotors and is particularly concerned with control and trim of suchaircraft.

The invention is especially adapted to a sustaining rotor havingautomatic means for compensating for differential lift effects atopposite sides of the rotor, especially those differential lift effectswhich are set up as a result of translational flight of the aircraft,during which the blade at the advancing side of the rotor experiencesvery much higher air speed than the blade on the retreating side.Moreover, the invention is especially adapted to an aircraft equippedwith such a rotor and with flight control means operating to shift thelift line of the rotor for maneuvering.

The invention is particularly adapted to that type of sustaining rotorin which the blades are pivotally connected with the hub with freedomfor movement in the flapping" sense for automatic compensation ofdifferential lift. Differential lift compensation, especially byautomatic flapping movements of the blades during translational flight,results in a shifting of what may be termed the virtual axis of rotationof the rotor (though actually it is a shifting of the approximate axisof rotation of the blades of the rotor, without altering the location ofthe hub thereof). This results in movement of the rotor lift line orvector to difierent angular positions at different translational flightspeeds. rotors of the type having flappingly pivoted blades, to whichthe invention is particularly adapted, at high speed translationalflight both the virtual axis and the lift line pass the center ofgravity of the aircraft farther ahead thereof than in low speedtranslational flight or in vertical ascent or descent. Therefore, indifferent conditions of flight the virtual axis and the lift line arevariously angled with respect to the physical axis of the rotor hub.

Variations in the position of the virtual axis of the rotor with respectto the physical axis of the hub causes the blades to experience greateror lesser flapping movements with respect to the hub (or equivalentdifferential lift compensating movements) and this in turn results inthe transmission of vibrations or fluctuating loads to the pilot'scontrol.

With the foregoing in mind, it is one of the primary objects of thepresent inventionto provide a rotor employing differential pitch changefor shifting the lift line to maneuver the craft Thus, with and totiltably mount the rotor hub so that the physical axis of the hub may beadjustably tilted "into approximate coincidence with the virtual axis ofthe rotor and with the rotor lift line in different flight conditions.The virtual axis and the lift line ordinarily coincide or lie close toeach other.

Since the major excursions of the virtual axis and the lift line takeplace in a fore and aft plane (as a result of variation in thedifferential lift effects at different flight speeds), the inventionprovides for tilting of the rotor hub in a fore and aft plane so thatthe physical axis of the hub may be swung forwardly (below the rotor)during high speed translational flight, at which time the virtual axisalso swings forwardly below the rotor.

The invention also provides controllable means for periodic differentialchange of blade pitch and for the tilting of the hub, each of whichcontrollable means is arranged to permit actuation thereof withoutappreciably altering the adjusted setting of the other.

How the foregoing and other objects and advantages are secured willappear more clearly from the following description, referring to theaccompanying drawings which illustrate an embodiment of the invention asapplied to an aircraft having a single sustaining rotor of theautorotatable type, with blades which are I flappingly pivoted to therotor hub.

In considering the drawings, it is to be kept in mind that the inventionis applicable to various types of aircraft equipped with one or moresustaining rotors, whether or not the rotors are always autorotated. Forinstance, the invention is applicable to helicopters or machines inwhich the rotor or rotors, though perhaps autorotatable under certainconditions, are normally continuously driven; in which event, of course,provision must be made for counteracting the rotor drive torque effect.Still further the invention is applicable to sustaining rotors (whetherof the helicopter or of the autorotative type) in which some means otherthan pure flapping pivots are employed for compensation for differentiallift effects.

- Referring to the drawings:

Figure l is a fragmentary side elevational outline view of a portion ofan aircraft with a rotor hub supported thereon, the view particularlyillustrating various of the controls provided in accordance with theinvention;

Figure z is a vertical sectional view through the rotor hub and blademounting and also through portions of the control mechanisms;

Figure 3 is a top plan view of certain parts of the rotor hub, the view.being taken as indicated by the line 3-3 applied to Figure 2; and

Figure 4 is an elevational view of certain parts of the controlconnections taken as indicated by the line 3-3 of Figure 2.

A portion of the fuselage or cabin outline appears in Figure 1 at 5, thepilot's seat being shown at 5. Connected with the fuselage framing anddisposed above the cabin is a rotor support including upwardlyconverging pylon members I and 8. "These members are joined by an apexmember 9 to which a non-rotative hub support I is connected by means ofa tilting pivot or fulcrum I011.

The rotative hub H is of hollow cylindrical form and is journaled in thenon-rotative part by bearings such as those shown at I2-l2. The rotorblades are plvotally connected with the hub II as described hereinafter.

A. portion of a rotor drive mechanism is illustrated in Figures 1 and 2.Thus, the hub l carries a ring gear l3 adapted to be driven by pinion itwhich is journaled in a casing l5 formed as a part of the hub support.The shafting I 6 for driving the pinion desirably incorporates flexibleand telescopic joints i1 and i8. At its lower end the shaft i6 ispreferably connected with an enine (not shown) which, in the case of amachine equipped with an autorotatable rotor, normally serves to drive aforward propulsion airscrew to induce translational flight. In the caseof the autorotatable rotor, the rotor drive mechanism just described ispreferably employed only for the purpose of starting the rotor beforetake-off, and for this purpose such a rotor drive ordinarilyincorporates both a manually operable clutch for connecting anddisconnecting the drive and also a freewheeling or overrunning clutch.Suitable examples of such clutches appear in Patent No. 1,999,636 ofJoseph S. Pecker, issued April 30, 1935. Moreover, in the case of anautorotatable rotor, as here shown, the'rotor drive may be employed tooverspeed" the rotor to a point above its normal autorotative speed toprovide for storage of kinetic energy with the rotor blade pitch reducedto zero. Upon disconnection of the rotor drive and increase of the bladepitch the kinetic energy may be converted to lift and the machine causedto effect vertical or jump takeoff in the manner more fully disclosed incopending application of Juan de la Cierva, Serial No. 738,349, filedAugust 3, 1934, corresponding to British Patent No. 420,322.

The control and trimming mechanism of the present invention isapplicable regardless of the method of take-oil? employed or whether therotor is mechanically driven only in preparation for take-oil or fornormal flight. The invention, however, is especially useful in aircraftcapable of operation over a range of conditions from vertical flight tohigh speed translational flight, since that type of machine experiencesmaximum excursions of the virtual axis of the rotor.

In the arrangement shown (see Figure 2), each of the rotor blades isconnected with the hub I l by means of three pivots. The root end orshank of a blade appears at 19 at the left in Figure 2, the same beingjournaled by bearings 2020 in a sleeve 2|, the bearings 20 providing apivot for movement of the blade about its own longitudinal axis, 1. e.,movement in the pitch change sense. The sleeve 2| has a pair ofinwardlyproiecting iii) apertured lugs 22 which cooperate with one ofthe two pairs of pivots formed on a universal block 23, thus providing aflapping pivot axis on which the blade is free to flap in a directiongenerally transverse its mean rotative path of travel. The other pair ofpivots 2424 of the universal block cooperate with a pair of aperturedears 25-25 on members 26 and 21, connected to or formed integrally withthe hub member H. The pivots 24--24 provide a drag pivot axis for theblade, i. e., an axis providing freedom for blade movement fore and aftwithin the rotative path of travel.

The arrangement of blade mounting pivots and associated parts is not apart of the present invention per se, and is therefore only brieflydescribed herein. For further details, reference may be made tocopending application of Cyril George Pullin, Serial No. 316,330, filedJanuary 30, 1940, issued as Patent 2,325,632 on August 3, 1943.

Change of blade pitch is secured by means of a series of connectionsextended within the blade mounting pivots and thence through the hub tothe pilot's controls. Thus, as seen in Figure 2, a part 28 is keyed andpinned to the blade shank I9 and projects inwardly therefrom to connectwith member 29 through the universal joint 30 which is centralized withrespect to the point of intersection of the flapping and drag pivot axesprovided by the universal joint 23. At its inner end, within the hollowhub II, the member 29 carries an arm 3| which, as best shown in Figure3, is curved part-way around the hub, terminating at a pointapproximately from the axis of the associated blade. Link 32 has aspherical joint connection 32a with the free end of arm M, the link 32extending downwardly therefrom to connect with pin 33, this connectionalso taking the form of a spherical joint 32b.

It will be seen that raising and lowering of the links 32 will causemembers 29 and 28 to oscillate and thereby change the blade pitch. Thismovement is effected by a. tiltable and vertically displaceable swashmember 34 on which the pins 33 are mounted, the swash member beingrotatable on spindle 35. Relative rotation of the swash member 34 andhub II is restrained by pairs of vertical guides 32c mounted on the huband cooperating with the eye surrounding joint 32b. The spindle 35 ismounted for universal tilting movement about intersecting axes providedby the universal joint parts 36, 31 and 38. The members 38 of thisuniversal joint take the form of pivots which mount the universal on thesleeve 39, the lower end of which has a coarse external thread engaginga complementary internal thread formed on sleeve 49. Sleeve 40 isjournaled in a non-rotative cylindrical part 4| of the hub support 10.Rotation of sleeve 39 may be prevented by any suitable means such as oneor morefingers 39a engaging vertical guides 39b.

Rotation of sleeve 49 thus causes the member 39 to be raised or loweredand this, in turn, effects simultaneous increase or decrease of theaverage pitch of all blades of the rotor, upward movement of member 39effecting increase of pitch and downward movement effecting decrease ofpitch when the rotor rotates in a. clockwise direction when viewed fromabove (see arrow R in Figure 3), as is contemplated in the disclosedembodiment. Rotation of the sleeve 40 is controlled by a cable-42 whichengages a drum or lower extension 43 formed as a part of sleeve 40. Thecable 42 may be actuated by any suitable manual control device, such asa lever or crank (not shown). This simultaneous pitch control may beemployed to vary the lift or thrust of the rotor and also reduce thepitch'angle of the blades to zero for purposes of driving the rotor onthe ground in preparation for jump take-off in the manner abovedescribed.

As hereinbefore indicated, the present invention contemplates periodicdifferential pitch change of the blades to shift the lift line of therotor for flight control or maneuvering purposes. Periodic differentialpitch change is brought about by tilting the lower extension 35a (seeFigure 2) of the universally mounted spindle which supportsthe swashmember 34. The lower end of the extension 35a is reduced to provide apin 44 to which lateral and longitudinal control connections arecoupled, as will now be described.

Referring first to Figure 1, it will be seen that a control column orstick 45 is provided adjacent the pilot's seat, this stick dependingfrom a rockshaft 46 and pivoted thereto as at 41. The rockshaft may bejournaled in fixed parts 48 and 49. Longitudinal control is effected byfore and aft swinging movement of the stick 45. This movement istransmitted through link 50 having a ball connection 51 with the stickand a universal connection 52 with one arm 53 of a bellcrank pivoted ona fixed part at 54. The

other arm 55 of this bellcrank is connected by a link 56 with an arm 51of another bellcrank pivotally mounted at 58 on a fixed support 58a (seeFigures 1, 2 and 4). Link 59 is connected with the last mentionedbellcrank by means of a spherical or ball joint 60 and extends therefrom toward the lower end of member 35a. The connection between member35a and link 59 comprises a joint part having a pair of apertured forkprongs 6I-6I, cooperating with pin 44, and further having a pivot 62cooperating with link 53.

By means of this linkage, fore and aft movement of the control stick 45causes the swash member 34 to be tilted in a fore andv aft plane aboutthe axis of pivot 36.

The connections for lateral control are as follows:

Referring first to Figure 1, lateral movement of the control stick 45causes oscillation of the rockshaft 46. This motion is converted topushpull movement of the upright link 63 which is connected with therockshaft 46 through a laterally projecting arm 64.

Referring to Figure 4, it will be seen that the upper end of link 63 ispivoted to an arm 65 of a bellcrank, the other arm of which is pivotedat 66 to the non-rotative hub support 10. Here, again, the bellcrank isconnected with the pitch control member 35a by means of a link 61 havinga ball connection 68 with the bellcrank. At its other end the link 61 ispivoted to a member 63 having a single apertured lug 10 which, as bestseen in Figure 2, engages the pin 44 and lies between the pair of prongs61-61. of the longitudinal control connection.

Lateral movement of thecontrol stick 45 thus effects tilting movement ofthe swash member 34 in a lateral plane.

Tracing through the longitudinal and lateral control connections willshow that forward movement of the control stick 45 (to the left whenviewed as in Figure 1) causes tilting movement of the swash memberdownwardly at its-forward edge. The converse takes place with rearwardmovement of the control stick.

Movement of the control stick to the pilots left causes upward movementof the swash member 34 at the right-hand side thereof, and conversely,movement of the control stick to the pilots right causes upward tiltingmovement of the swash member at the left side. thereof.

With the direction of rotation of the rotor above referred to (clockwisewhen viewed from above) and with pitch control arms 3| for the bladnextending approximately 90 around the hub, the above described movementsof the control connections provide for periodic differential pitchchange in the following senses:

When the control stick is moved forwardly, the blade at the advancingside of the rotor experiences its maximum decrease of pitch and theblade at the retreating side of the rotor experiences its maximumincrease of pitch. This relationship is inverted when moving the controlstick rearwardly.

As to lateral control, movement of the control stick to the pilot's leftcauses the blades to attain their maximum increase of pitch when theypass at the front of the rotor and their maximum decrease of pitch whenthey pass at the rear of the rotor. Control stick movement to thepilot's right produces the converse effect.

With a rotor incorporating flappingly pivoted blades, as hereinillustrated, the foregoing provides instinctive" control in pitch-androll for reasons more fully brought out in the copending application ofJuan de la Cierva, Serial No. 698,- 372, filed November 16, 1933,corresponding to British Patent No. 410,532. In other words, the controlhook-up provides a nose-down moment upon movement of the control stickforward; a nose-up moment upon movement of the control stick rearwardly;a rolling moment to the left when the stick is moved to the left; and amoment to the right with corresponding movement of the stick.

With respect to the pitch control connections above described, it is tobe kept in mind that with other types of blade pivot arrangements, a

somewhat different sense of control hook-up may be necessary.

As hereinbefore mentioned, operation of the aircraft in different stylesof flight and especially operation at different translational flightspeeds causes the virtual axis of the rotor and the rotor lift line toswing or shift with respect to the center of gravity of the craft andalso with respect to the physical axis of rotation of the hub. Theovercome certain disadvantages of this travel of the lift line, thepresent invention provides for mounting the rotor on a tilting fulcrumI00, above described, so that the physical axis of the hub may bebrought to a approximately coinciding with the longitudinalpositionapproximately coinciding with the longitudinal position of thevirtual axis and of the lift line in different styles of flight.'

The control means provided for this longitudinal tilting of the hubappears in Figures 1, 2 and 4. As seen in Figure 1, a crank II isarranged above the pilot's seat and provides for rotation of the shaft12. The shaft rotates sprocket 13 (see Figure 2) which actuates chain 14cooperating with another sprocket 15 mounted on a shaft I6 which isjournaled in a fixed casing 11. Universal joint I8 serves to coupleshaft 16 with an internally threadedsleeve 19 which cooperates with thethreaded rod projecting downwardly from a yoke 8| (see Figure 4). Yoke3| is connected with the hubsupport In by the pivots 82-82.

Rotation of the'hand crank ll thus efiects tilting movement of the hubabout the axis of trunnion Illa and this adjustment is preferablyemployed as a trimming device to meet the different conditions offlight. With this in mind, the threading between members 19 and 80 ispreferably irreversible, so as to maintain any desired setting.

The invention thus provides for variably shifting the physical axis ofthe hub to maintain approximate coincidence thereof with the virtualaxis of the rotor and with the lift line. This reduces flappingmovements of the blades with respect to the hub and correspondinglyreduces certain vibrations or fluctuating loads which are otherwisetransmitted to the pilot's controls.

Attention is called to the fact that the several control connections forsimultaneous pitch change, for differential pitch change, and fortilting of the hub are all arranged so that actuation of any one doesnot appreciably alter the setting of either of the others. This resultis achieved by the arrangement of bellcranks, links and pivots for thevarious operating connections as illustrated. Of particular importancein this connection is the arrangement of bellcrank 51 and the associatedlink 59. With this bellcrank pivoted on a fixed support and with thetrunnion Illa for hub tilting located close to the horizontal planecontaining the lower end of arm 35a, adjustable tilting of the hub maytake place without appreciable change of blade pitch. This action mayreadily be appreciated from inspection of Figure 2, from which it may beseen that tilting of the hub about the trunnion Ia will not cause thepitch control arm 35a to swing to any appreciable extent, said am beingretained substantially in its adjusted angular position (in the fore andaft plane) by link 59.

The arrangementof bellcrank 65 for lateral control is also such thatfore and aft tilting of the hub about the trunnion Illa will notappreciably alter the lateral pitch control adjustment.

This application is a substitute for my appli-- cation Serial No.349,049, filed August 1, 1940.

I claim:

1. In an aircraft having a bladed sustaining rotor, mechanism forshifting the lift line'of the rotor to'maneuver the craft includingcontrollable means providing for periodic differential change of bladepitch, means mounting the blades on the rotor hub with freedom formovement to compensate for differential lift effects in translationalflight whereby the rotor lift line moves to different positions atdifferent translational flight speeds, and controllable means fortilting the physical axis of the rotor hub to bring said axis intoapproximate coincidence with the rotor lift line in different flightconditions, the first-mentioned means being constructed and arranged toaccommodate rotor hub tilting without being detrimentally affectedthereby.

2. In an aircraft having a bladed sustaining rotor, mechanism forshifting the lift line of the rotor to maneuver the craft includingccntrollable means providing for periodic differential change of bladepitch, means mounting the blades on the rotor hub with freedom formovement to compensate for differential lift effects in translationalflight whereby the rotor lift line moves to different positions atdifferent translational flight speeds, and controllable means fortilting the physical axis of the rotor hub to bring said axis intoapproximate coincidence with the rotor lift line in different flightconditions, each of said two controllable means being actuable withoutappreciably altering the effective setting of the other.

3. In an aircraft having a bladed sustaining rotor, mechanism forshifting the lift line of the rotor to maneuver the craft includingcontrollable means providing for periodic differential change of bladepitch, means mounting the blades on the rotor hub with freedom forflapping movement whereby the rotor lift line swings forwardly withrespect to the center of gravity of the craft with increase in forwardflight speed, and controllable means for tilting the physical axis ofthe rotor hub in the fore and aft sense to bring said axis intoapproximate coincidence with the rotor lift line in different flightconditions, the first-mentioned means being constructed and arranged toaccommodate rotor hub tilting without being detrimentally affectedthereby.

4. In an aircraft having a bladed sustaining rotor, mechanism forshifting the lift line of the rotor to maneuver the craft includingcontrollable means providing for periodic differential change of bladepitch, means mounting the blades on the rotor hub with freedom formovement to compensate for differential lift effects in translationalflight whereby the rotor lift line moves to different positions atdifferent translational flight speeds, controllable means forsimultaneously raising and lowering the average pitch of all blades ofthe rotor, and controllable means for tilting the physical axis of therotor hub to bring said axis into approximate coincidence with the rotorlift linein different flight conditions, each of said three controllablemeans being actuable without appreciably altering the effective settingof either of the others.

5. In an aircraft having a sustaining rotor with flappingly pivotedblades, wherein the lift line of the rotor swings forwardly with respectto the center of gravity of the craft with increase in forward flightspeed, controllable means for periodically differentially varying therotor blade pitch angles to shift the lift line of the rotor to maneuverthe aircraft, and controllable means for tilting the rotor hub, thefirst-mentioned means being constructed and arranged to accominodaterotor hub tilting without being detrimentally affected thereby.

6. In an aircraft having a sustaining rotor with flappingly pivotedblades, wherein the lift line of the rotor swings forwardly with respectto the center of gravity of the craft with increase in forward flightspeed, controllable means for periodically differentially varying therotor blade pitch angles to shift the lift line of the rotor to maneuverthe aircraft, and controllable means for tilting the rotor hub in thelongitudinal plane of symmetry of the craft, the first-mentioned meansbeing constructed and arranged to accommodate rotor hub tilting withoutbeing detrimentally affected thereby.

7. In an aircraft, a bladed sustaining rotor having means ofcompensation for differential lift effects in translational flight,controllable means for effecting periodic differential change of bladepitch to shift the rotor lift line for maneuvering the craft, andadjustable means fortilting the actual rotor axis to various fixedsettings to place said axis in approximate coincidence with the rotorlift line in different positions of the latter, the said controllablemeans being constructed and arranged to accommodate rotor axis tiltingwithout being detrimentally affected thereby.

8. In an aircraft having a bladed sustaining rotor including arotor axismember, a controllable pitch-changing system adapted to effect bladepitch change in synchronism with the rotational period of the rotor tocontrol the rotor thrust line position, a pivotal mounting for tiltingmovement of the rotor axis member to various positions according todifferent flight conditions, and rotor-tilt accommodating meansincorporated in the pitch changing system and adapted inherently toprevent appreciable disturbance of a given pitch control condition bythe normal movements of the rotor axis member upon its pivotal mounting.

9. In an aircraft having a bladed sustaining rotor. means for shiftingthe lift line of there-- tor to maneuver the craft includingcontrollable means providing for periodic differential change of bladepitch, means mounting the blades on the rotor hub with freedom formovement to compensate for difierential lift effects in translationalflight whereby the rotor lift line moves to different positions atdifferent translational flight speeds, and controllable means fortilting the physical axis of the rotor hub to bring said axis into aproximate coincidence with the rotor lift line in different flightconditions.

10. In an aircraft having a bladed sustaining rotor incorporating meansof compensation for differential lift efl'ects in translational flightand having a rotor driving system, said rotor comprising a rotor axismember, a controllable pitchchanging system adapted to effect cyclicblade pitch change in synchronism with the rotationai period ofthe-rotor to control the rotor thrust line position, a pivotal mountingfor tilting movement of the rotor axis member to various positionsaccording to diflerent flight conditions, rotor-tilt accommodating meansincorporated in said pitch-changing system and adapted inherently toprevent appreciable detrimental disturbance of a given pitch controlcondition by the normal movements of the rotor axis member upon itspivotal mounting, and a blade pitch control adapted to raise and lowerthe mean rotor blade pitch for altering total rotor thrust under a givenrotor drive condition, including control connections operative by thepilot independently of the cyclic pitch change and constructed andarranged to prevent appreciable detrimental disturbance oi. mean bladepitch by normal rotor axis tilting.

HAROLD F. PITCAIRN.

CERTIFICATE-OF CORRECTION. Patent No. 2, 52,5L 2. I June 27, 191m.

' HAROLD F. PITCAIRN.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 5,second wlumn, line 51 for the word "The' read --'1o--; line 59; strikeout the words "approximately coinciding with the longitudiml'F; and.that the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the-Paten-tOffiCe.

Signed and sealed this 15th day of August, A. n. i9hl Leslie Frazer(Seal) Acting'oommiesioner of Patents.

